Method of protecting electric blasting caps



Sept. 13, 1955 c. M. BLACKBURN ET AL 2,717,551

METHOD OF PROTECTING ELECTRIC BLASTING CAPS Filed Nov. 16, 1950DNVENTORSZ CHARLES M. BLACKBURN FREDERICK R. S AVEY "7 ATTORNEYS.

United States Charles M. Blackburn and Frederick R. Seavey, Alton, Ill.,assignors to Olin Mathieson Chemical Corporation, a corporation ofVirginia Appiication November 16, 1950, Serial No. 195,974

1 Claim. (Cl. 10228) This invention relates generally to electricblasting caps, and particularly to the treatment, prior to packaging, ofthe terminal portions of the lead wires for such blasting caps.

The ordinary electric blasting cap of commerce is provided with longlengths of lead wire, the free ends of which are adapted to be connectedinto the firing circuit when the blasting cap is placed in position todetonate explosive.

In the packaging of electric blasting caps for shipment and handling, itis important to protect the cap from the possibility of accidentaldetonation which might occur by virtue of the lead wires coming incontact with stray electric currents and other sources of electricalenergy. Protection of the caps in this respect involves shunting orotherwise temporarily, i. e., for the duration of the shipping andhandling process, electrically connecting together the respective leadwires near their free ends, as well as the provision of an insulatingcover about any naked portions of the wire.

The object of the present invention, generally stated, is to provide amethod of treating the lead wires of electric blasting caps andpackaging the same whereby to protect the device in shipment and tofacilitate its connection into a firing circuit.

Another object of the invention is to provide an electric blasting capwherein, as the shunt is removed, the lead wires are bared of insulationat their terminal portions.

Other objects will become apparent to those skilled in the art when thefollowing description is read in connection with the accompanyingdrawings, in which:

Figure 1 is a view in side elevation of apackaged electric blasting capconstructed in accordance with the present invention, part of saidpackage being shown in section to reveal the relationship of the severalparts;

Figure 2 is an enlarged detail view showing the free ends of the leadwires of the blasting cap shown in Figure 1;

Figure 3 is an end view of the shunting device shown in Figure 1;

Figure 4 is a view corresponding to Figure 1, but showing a differentembodiment of the invention; and

Figure 5 is an enlarged detail view of the free ends of the lead wirestreated as shown in Figure 4.

The present invention contemplates that the lead wires of the usualelectric blasting cap have their free ends treated so that theinsulation covering the terminal two or three inches is severed from theinsulation covering the balance of the wires, and the terminal portionslightly separated from the main portion by slipping the separated piecelengthwise of the wire so that the separated portion overhangs the endof the conductor. A gap between the terminal portion of insulation andthe main portion of insulation is thus formed whereat the conductorswithin the lead wires are bare. The invention contemplates that the leadwires be electrically shunted at said gap, and this may be accomplishedby engaging the two bared conductors and suitably but temporarilysecuring them in enatent C) gagement, or by applying an auxiliaryconductive clip to the bared conductors at said gap. In either event, itis desirable to surround the connection between the bared conductorswith a protective member of non-conducting material in order to preventcontact with live electrical parts.

the member holding the wires together may be gripped and slipped endwiseof the wirestoward their free end-to straight, as used in connectionwith the terminal por tions of the lead wires in this specification andthe appended claims, is not used in its geometric sense, but ratherconnotes the freedom from kinks or abrupt turns or bends, which wouldinterfere with the free slipping of the original insulation coveringfrom the wires.

Referring now to Figures 1, 2, and 3 of the drawings for an illustrativeembodiment of the invention, an electric blasting cap 1 of any suitableconstruction is provided with apair of lead wires 2 and 3, which are ofsubstantial length and coiled about a tubular spool 4 in amanner wellknown to those skilled in the art.

The lead wires 2 and 3 are of the type generally employedv in the artwherein a conductor strand is encased. in insulation, which may beplastic, rubber textile, I or any other suitable material, severedincrements of which retain a tubular form;

The invention contemplates that the free ends of the lead. wires 2. and3 be treated so as to separate. the insulation at the terminal portionsthereof from the insulation upon the balance of the wires. 'Theoperation is shown most clearly in Figure 2. The two or three inches oflead wire at the extremities thereof is herein referred to as theterminal portion, by which is meant the. portion of the wire usuallystripped of its insulation in. order to make the electrical connectionsinto the firing; circuit. Between the terminal portion and the mainportion of the. lead wires, the insulation is cut, as for example, atlines 5 and 6 of wires 2 and 3, respectively. The cutting operation maybe accomplished with any of the well known tools available for thepurpose, but is preferably done in such manner that the conductorelement within the lead wires is not mutilated. The lines of cut 5 and 6permit the short sections of insulation 7 and 8 about the terminalportions of wiresv 2 and 3, respectively, to be slipped lengthwise ofthe wires, thus forming a gap 9 between the shoulders of insulationformed by the cuts 5 and 6 between the main portions of insulation andthe terminal portions 7 and 8. At the gap 9, the conductor within leadwire 2 is bared of insulation, as shown at 10, and the conductor withinlead wire 3 is bared of insulation, as shown at 11. When the portions ofinsulation 7 and 8 are slipped lengthwise as above indicated, the endsthereof overhang and thus protect the tips 12 and 13 of the conductorswithin the lead wires 2 and 3, respectively. As above indicated, it isdesirable to maintain the conductors within the terminal portions ofinsulation 7 and 8 straight.

After the insulation on the terminal portions of the lead wires 2 and 3has thus been separated from the insulation on the main portionsthereof, the wires are connected together at sections 10 and 11. Asshown in Figures 1 and 3, the connection takes the form of a splitmetallic cup 14, which is fitted Within spool 4. The cup 14 has itsbottom split to provide two spring members 15 and 16, which will yieldsufiiciently to per- Patented Sept. 13, 1955 Furthermore, it isdesirable to form the connection. between the lead wires at the gap insuch manner that mit the lead wires to be passed therebetween. As shownin the drawings, the parts 15 and 16 are flared in a direction such thatthe force exerted incident to forcing the tip of the lead wires inwardlytherethrough readily separates the parts 15 and 16, but the reversemovement tends to draw said parts together. The terminal portions of thelead wires are passed through cup 14 so as to lie on the interior ofspool 4 with the parts 15 and 16 engaging the bared conductors at 10 and11. Thus, when the cup 14 is formed of conductive material, the leadwires are thereby electrically shunted.

The extremities of the lead wires may be passed through the cup 14before the latter is inserted in spool 4, or afterwards, as is desired,it being unnecessary to rigidly secure the cup 14 within the spool 4.When the user is readyto connect the lead wires 2 and 3 into the firingcircuit, the spool 4 may be gripped in one hand in such manner that athumb or forefinger prevents withdrawal of cup 14 from the interior ofthe spool. With the adjacent portions of lead wires 2 and 3 gripped inthe other hand and pulled in the withdrawing direction, it isevidentthat the tips of spring members 15 and 16 will engage the shoulderformed on terminal portions 7 and 8 of the insulation by cuts 5 and 6and prevents the latter from being withdrawn concurrently with the leadwires. Hence, as the wires are withdrawn, the terminal portions ofinsulation 7 and 8 are completely removed from the conductors thereincontained and, as the wires are' withdrawn from the spool 4, they areready for connection into the firing circuit without any furthertreatment.

In the embodiment shown in Figures 4 and 5, the lead wires 2 and 3 aretreated in the same manner as described above with reference to Figure2, so as to provide terminal portions of insulation 7 and 8 spaced fromthe main portions of insulation on wires 2 and 3. In this embodiment,however, the electrical connection of the lead wires at the gap betweenthe two separated portions of insulation is accomplished by bringing thewires into physical engagement with each other at the aforesaid gap.With the wires in physical contact, the same may be temporarily fastenedtogether in any suitable way, as for example, by tying them with astring, thread, or ribbon, or by applying a sticker, clip, or clamp, soas to maintain the bared parts in electrical connection during theprocess of shipping and handling. As shown in the drawings, the baredsections of conductor are held in contacting relation by being bound bya layer of non-conductive thread 20. The non-conductive thread 20 notonly assures the maintenance of electrical contact between the twoconductors, but prevents contact therewith of live electrical parts. Theinvention is,

however, not limited to the utliization of non-conductive material forconnecting the parts together in this manner, but, when conductivematerial is utilized for this purpose, it is desirable to tuck theterminal portions of the lead wires, including the binding 2% into theinterior of spool 4, in contrast to the exterior position shown inFigure 4. Moreover, when the tie is of conductive material, it isunnecessary to hold the bared sections of wire in physical contact witheach other.

When it is desired to connect the blasting cap into its firing circuit,the binding 20 may be gripped between the thumb and forefinger of onehand, while the main portions of the lead wires are gripped in the otherhand, and the two drawn apart, thus concurrently stripping the leadwires 2 and 3 not only of the binding 21), but of the terminal portionsof insulation 7 and 3. Thus in both embodiments the outer ends of thelead wires are protected by the overhanging insulation, the baredincrements are electrically connected together, and the latter areprotected from contact with live electrical members either by beingenclosed within the spool 4, or by being wrapped with non-conductivematerial 20.

From the foregoing description those skilled in the art should readilyunderstand the construction, operation, and advantages of the invention.piete embodiments have been disclosed in detail and other alternativessuggested, it is not to be understood that the invention is limited tothe details described. On the contrary, it is to be distinctlyunderstood that the foregoing disclosure is merely for illustrativepurposes, and

that such modifications and variations thereof as do not depart from thespirit of the invention are contemplated by and within the scope of theappended claim.

Having thus described the invention, what is claimed and desired to besecured by Letters Patent is:

The method of protecting electric blasting caps having insulated leadwires which comprises making a cut through the insulation on the leadwires to separate the insulation on the terminal portions of the leadwires from the insulation on the remainder of the wires, slipping theseparated terminal section of insulation endwise of the wires to bare ashort increment of wire, all without removing the insulation from thewires, and, with the separated section of insulation overlapping theends of the wires, electrically short-circuiting the bared increments ofthe lead wires, and packing the caps with the short-circuited incrementsenclosed by non-conductive material.

References Cited in the file of this patent UNITED STATES PATENTS1,983,141 McFarland Dec. 4, 1934 2,062,189 Olin et a1 Nov. 24, 19362,218,170 Hunt Oct. 15, 1940 2,649,735 Feild Aug. 25, l953 FOREIGNPATENTS 336,423 Great Britain Oct. 16, 1930 While two com-

